Abnormalities of motor cortex excitability are related to clinical symptoms in patients with cerebellar ataxia

Objective: To examine the correlation between clinical fea-tures and transcranial magnetic stimulation (TMS) parame-ters of motor excitability in cerebellar patients.Background: Abnormalities of primary motor cortex (M1)excitability have been demonstrated in patients with cerebellarataxia by means of TMS. These alterations point to changes inthe activity of different M1 neurotransmitters populationsrelated to cerebellar dysfunction.Methods: We investigated the short-latency afferent inhibition(SAI), the duration of cortical silent period (CSP) to single-pulse TMS and the long-latency intracortical inhibition (LICI)to paired-pulse TMS in the intrinsic hand muscles of ninepatients with pure cerebellar ataxia. We evaluated whetherthese TMS parameters were correlated to measures of ataxia,scored with the International Cooperative Ataxia Rating Scale(ICARS), using Spearman’s correlation test (P < 0.05).Results: SAI was significantly correlated to upper-limb ICARSscore (P < 0.02) but not with total score. The other TMSmeasures were not significantly correlated with clinical scores.Conclusions: Different M1 inhibitory functions are impairedin cerebellar ataxia. Some of these functions are involved inearly stages of the disease. On the other hand, the M1 exci-tability to afferent inputs may decline with disease progres-sion. The clarification of the importance of these factors in thepathogenesis of cerebellar syndromes may be of diagnosticvalue. The present results may represent the background fornew therapeutic approaches to cerebellar ataxia.